1. Field
The invention relates to a modified diene elastomer comprising predominantly the diene elastomer functionalized at the chain end by an amine functional group and coupled in the middle of the chain by a silanol group. The invention also relates to a process for the preparation of such a modified diene elastomer, to a composition comprising it, and to a semi-finished article and a tire comprising this composition.
2. Description of Related Art
Now that savings in fuel and the need to protect the environment have become a priority, it is desirable to produce mixtures having good mechanical properties, in particular good stiffness and a hysteresis which is as low as possible in order to be able to process them in the form of rubber compositions which can be used in the manufacture of various semi-finished products participating in the composition of tire casings, such as, for example, underlayers, sidewalls or treads, and in order to obtain tires having a reduced rolling resistance.
The reduction in the hysteresis of the mixtures is an ongoing objective which has, however, to be done while retaining the suitability for processing, in particular in the raw state, of the mixtures.
Many solutions have already been experimented with in order to achieve the objective of fall in hysteresis. Mention may in particular be made of the modification of the structure of diene polymers and copolymers for the purpose of polymerization by means of functionalization agents or else the use of functional initiators, the aim being to obtain a good interaction between the polymer, thus modified, and the filler, whether carbon black or a reinforcing inorganic filler.
In the context of the mixtures comprising a reinforcing inorganic filler, provision has been made to use diene copolymers functionalized by silanol groups.
Mention may be made of Patents FR 2 951 178 B1, FR 2 915 202 B1 and EP 778 311 B1, which describe the use of diene polymers functionalized by a silanol group at the chain end or in the middle of the chain in order to decrease the hysteresis of reinforced rubber compositions based in particular on a reinforcing inorganic filler. In Patent FR 2 915 202 B1 in particular, it is mentioned that the functionalization in the middle of the chain makes it possible to improve the raw processing, in comparison with a functionalization at the chain end. More recently, Patent Application WO2009077837A1 describes elastomers functionalized by a silanol group at one chain end and by an amine group at the other chain end. These elastomers are also described as being able to be combined with star-branched elastomers, in particular elastomers star-branched by silicon or tin. However, the combinations illustrated result in a reinforced rubber composition, the processing/hysteresis compromise of which is not satisfactory for application in tires.
Specifically, it turns out that the compositions described in the prior art do not always exhibit a satisfactory hysteresis, an acceptable processing and mechanical properties satisfactory for use in a tread.
For this reason, research studies have been carried out on other functionalization reactions for the purpose of obtaining rubber compositions having an improved raw processing/hysteresis/stiffness compromise.